Water heating apparatus

ABSTRACT

Disclosed is a solar water heating apparatus comprising a central tank and one or more outer layers wherein at least part of the exterior of the outermost layer is adapted to be exposed to the sun. The outer layers also form water pathways such that, when the tank is substantially filled with water, said water is able to circulate around a path formed by said central tank and the outer layers. A pulsing pump may help circulate the water. An auxiliary heating element may be also provided, such as a small gas burner.

This invention relates to water heating apparatus and in particularsolar water heating apparatus and/or combined solar and gas waterheating apparatus.

Simple water solar absorbers are not as effective in the Northern partof the temperate zone as they are in the Southern part of the same band.The length of sunshine or its strength limits severely the value formoney of these devices, in many cases realistically prohibiting theiruse or at the very least limiting their use to a small part of the year.Other problems like altitude, climatic considerations also add to theproblem. Too often, the water heated is too cool by the time it isneeded for use. In this case the cool water has to be reheated beforeuse, even more heat energy is to be used.

The invention in its various aspects aims to enable the provision of hotwater while avoiding or reducing one or more of the problems identifiedabove.

In a first aspect of the invention there is provided a solar waterheating apparatus comprising a central tank and one or more outerlayers, said outer layers also forming water pathways, wherein, whensubstantially filled with water, said water is able to circulate arounda path formed by said central tank and at least one of said one or moreouter layers, and wherein at least part of the exterior of the outermostlayer is adapted to be exposed to the sun, in use.

In a main embodiment said apparatus should be arranged such that wateris able to circulate between the outermost layer and the central tankvia any intermediary layers.

Pumping means may be provided to circulate the water. Said pumping meansmay comprise a pulsing pump. Said pump may be arranged to operatecontinuously or intermittently. Said apparatus may further comprisecontroller means to control said pumping means depending on sensed watertemperature at predetermined points in the apparatus.

Said tank and or the outer layers may be comprised of a plasticmaterial. Said plastic may be polypropylene or similar material.

Said tank and or the outer layers may be comprised of a metallicmaterial. Said metal may be copper or similar material.

Said at least one layers may comprise one or more outer tanks aroundsaid central tank. Said outer tanks may comprise water outlets/inlets atopposing points to adjacent tanks, to provide a tortuous path for saidwater to circulate.

Alternatively said at least one layers may comprise a hollow jacketwrapped at least once around said inner tank. The cross section of saidjacket may be in the shape of a symmetrically flattened round tube.Ideally said jacket is wrapped around the inner tank a plurality oftimes.

Said apparatus may comprise a cold water input and warm water output.Said warm water output is preferably drawn from said central tank. Inone embodiment this output is drawn from a point at or above halfwayfrom the bottom of the central tank. Said cold water input may also feedinto the central tank, preferably at the bottom, or alternatively intothe outermost layer.

Said apparatus may comprise insulation around its outside, of which atleast a portion of which is arranged to move so as to expose anuninsulated portion of the outside of said apparatus to allow for directsolar heating. Said insulation may be arranged to move based on the timeof day, readings from a temperature sensor, readings from a lightsensor, or a combination thereof. Alternatively said insulation maysimply be arranged to be moved manually.

Said apparatus may further comprise gas burner apparatus, said gasburner apparatus being substantially immersed in said tank. Said gasburner apparatus may be arranged, in normal use, to burn an amount ofgas comparable to that of a domestic pilot light flame. It may have afurther setting to burn gas at a greater rate for fast heating. Theflame of said gas burner apparatus may be located at a pointapproximately half way from the bottom of the central tank.

In a further aspect of that invention there is provided a combined gasand solar water heating apparatus comprising a central tank and a gasburner apparatus, said gas burner apparatus being substantially immersedin said central tank, and wherein at least part of the exterior of saidapparatus is adapted to be exposed to the sun so as to heat the contentsby solar energy, in use. As an alternative, said gas heating apparatusmay be replaced with an electric heating apparatus.

Said apparatus is preferably made of a plastic. Said plastic may bepolypropylene or similar material.

Said apparatus may further comprise one or more outer layers, said outerlayers also forming water pathways, wherein, when substantially filledwith water, said water is able to circulate around a path formed by saidcentral tank and at least one of said one or more outer layers. In amain embodiment said apparatus should be arranged such that water isable to circulate between the outermost layer and the central tank viaany intermediary layers. Pumping means may be provided to circulate thewater. Said pumping means may comprise a pulsing pump. Said pump may bearranged to operate continuously or intermittently. Said apparatus mayfurther comprise controller means to control said pumping meansdepending on sensed water temperature at predetermined points in theapparatus. Said at least one layers may comprise one or more outer tanksaround said central tank. Said outer tanks may comprise wateroutlets/inlets at opposing points to adjacent tanks, to provide atortuous path for said water to circulate. Alternatively said at leastone layers may comprise a hollow jacket wrapped at least once aroundsaid inner tank. The cross section of said jacket may be in the shape ofa symmetrically flattened round tube. Ideally said jacket is wrappedaround the inner tank a plurality of times.

Said apparatus may comprise a cold water input and warm water output.Said warm water output is preferably drawn from said central tank. Inone embodiment this output is drawn from a point at or above halfwayfrom the bottom of the central tank. Said cold water input may also feedinto the central tank, preferably at the bottom, or alternatively intothe outermost layer.

Said apparatus may comprise insulation around its outside, of which atleast a portion of which is arranged to move so as to expose aninsulated portion of the outside of said apparatus to allow for directsolar heating. Said insulation may be arranged to move based on the timeof day, readings from a temperature sensor, readings from a lightsensor, or a combination thereof. Alternatively said insulation maysimply be arranged to be moved manually.

Said gas burner apparatus may be arranged, in normal use, to burn anamount of gas comparable to that of a domestic pilot light flame. It mayhave a further setting to burn gas at a greater rate for fast heating.The flame of said gas burner apparatus may be located at a pointapproximately half way from the bottom of the central tank. If insteadan electric heating apparatus is used, said apparatus may use less powerthan 100 w, and possibly in the region of 50 w-80 w.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, by reference to the accompanying drawings, in which:

FIG. 1 shows a cross section of a domestic water heater according to anembodiment of the invention, comprising one micro furnace having asingle burner inside;

FIG. 2 shows a top view of the water heater shown in FIG. 1 showing thenon-dynamic insulation surrounding the apparatus;

FIG. 3 shows a cross section of a domestic water heater according to asecond embodiment whereby the cold mains supply is connected directly tothe central tank;

FIG. 4 is a top view of the apparatus of FIG. 3;

FIG. 5 shows a perspective view of the second embodiment of theinvention with the jacket rolled out; and

FIG. 6 shows a cross-section view A-A of the jacket for the secondembodiment.

FIG. 7 shows a different embodiment of the micro-furnace and burner.

FIG. 8 shows a different embodiment of the apparatus enabling water toflow tortuously into the central container using a different pathway.

FIG. 9 shows an embodiment of the jacket comprising spacers that keepthe layers at a distance apart.

FIG. 10 a shows the apparatus according to the embodiment described inFIG. 3 in more detail, including a dome at the top of the central tank.

FIG. 10 b shows the above view from cross-section S-S of FIG. 10 a.

FIG. 11 shows a pattern for manufacturing the first spiral layer of thejacket of FIG. 10.

FIG. 12 shows a side view of the formers placed on the same plane.

FIG. 13 shows the covered pattern to build the layers.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 is a cross sectional view of a water heating apparatus. 10. Itshows an outer container or tank 11 having (in this example) threefurther smaller containers 12, 13 and 14 fitted one inside the other ina “Russian-doll” style to form a multi-layered tank. Water space layers16, 17 and 18 are therefore formed between the outside and inside shellof adjacent containers. The outer shell of the inner containers issurrounded by a heat insulation material 15 (which is only shown on onehalf of the apparatus in FIG. 1). There are openings 35, 36 and 37 ineach of the inner containers 12, 13 and 14, the last of these, opensinto the innermost container via a chimney 29. The outermost container11 has a main inlet 41 connected to cold water supply 19 via solenoidswitch 30, and the innermost container has a main hot water outlet 32,which in turn connects to the sink 31 a, basin 31 b, bath 31 c orwashing machine 31 d taps and a release valve 38. There is also aconnection 21 between the outermost 11 and innermost 14 containers inwhich there is a pulsing pump 20.

A metal tube 40 is fitted through the axial vertical centre of thecontainers and accommodates a metal tube 22 to form a micro-furnace 60.The micro-furnace consists of a u-shaped secondary metal tube 22 intowhich there feeds a gas inlet 23 and air inlet 24. An air blower 25 maybe used to supply air to the micro-furnace. A constricted opening 27allows the expulsion of combusted gases. A removable cap 41 is placed onone end of the metal tube 40.

FIG. 2 shows insulation door 52 surrounding the tank to provide fullinsulation when in a closed position. The insulation door is not shownin FIG. 1 for the purpose of clarity. When in an open position, the doorenables at least 50% of the tank to be exposed to the outsideenvironment.

The tank apparatus, including the inner containers 12, 13, 14, ispreferably made of a polypropylene drum, but can be constructed usingcopper where it is more efficient, both in terms of cost andfunctionality, to do so. The tanks can be constructed using any heatconducting material, according to the size of the apparatus beingconstructed, which is the most economical and will perform or benefitthe purpose of the invention. The outside shell of the outermost drum 11forming the tank is preferably black to maximise the amount of heatgathered, by its exposed surface, from the sun. The shell can also becoated in a suitable material that aid to capture solar heat energy. Thetwo extremities of the tube 40 are sealed at the outermost drum usingsuitable grommets or slip rings (70) to make a waterproof connection.

The described arrangement provides a tortuous path for the water fromcold water supply 19, which enters the tank through inlet 41 at its top,then proceeds to flow through openings 35, 36 and 37, formed in theinner containers successively in their top ends and bottom ends, upchimney 29, and into the central inner container 14. A hot water outlet32 enables hot water to be drawn from the central container 14 to supplywater to various outlets, such as the sink 31 a, basin 31 b, dishwasher(not shown in FIG. 1), washing machine 31 d or bath 31 c in a house. Apipe 21 with pulsing pump 20 is connected from the central container 14to one of the water space layers 16, 17, 18 of the tank todraw/circulate water from the central container 14 to said layer 16, 1718. This example shows the pulsing pump 20 connected between the centralcontainer 14 and the outermost water space layer 16 of the tank. Thepulsed water, drawn from the central container 14, thereby pushes waterin the water space layers 16, 17 and 18 so that the water circulatesthrough the same tortuous path, described above.

In operation, water in the outermost layer 16 is heated using solar heatby exposing at least a portion of the exterior of the outermost tank 11to the sun's rays. There will also naturally be some heating, viaconduction, of the next layer 17, in contact (albeit via insulation) tothe solar heated layer 16. Pump 21 is operable to pump the cooler waterfrom inside the central reservoir 14 to the outer layer 16 where it willbe heated, the action of the pump forcing the already heated waterfurther along the tortuous path, to the other outer layers 17 and/or 18,and ultimately towards the centre. Ideally, the water temperature shouldbe measured at or near the bottom of the central reservoir 14, with thepump 20 controlled depending on this measured temperature, therebykeeping this measured temperature acceptably high.

Every time hot water is drawn off from the hot supply 32, the solenoidswitch 30 is triggered to replace substantially the same amount of coldwater from supply 19 in the tank. This also causes the heated water inthe outer layers 16, 17 and 18 to be pushed (by the mains supply 19)towards the central container 14, while the newly introduced watershould be in the outer layers, where it will be heated up by the sun.

In operation, the water in the central container 14 will have atemperature profile from top to bottom, the water being warmer at thetop of the central container compared to the bottom. Hot water, beingless dense than cold water, will always find its way on top of thecooler water, and move faster, in any situation. Hot water entering thecentral container 14 from opening 37 is directed to the warmer part ofthe central container by chimney 29. The chimney 29 creates a plume thatdelivers the hot water directly to the warmer top layers of the centralcontainer.

One advantage of having this tortuous flow of water into the centralcontainer is that the water does not lose a lot of its heat to itsadjacent layers by remaining stationary. Every time hot water is used,the solar heated water from the outermost layer 16 flows towards or intothe central container 14. Moreover, any heat that escapes from thecentral container is captured in the layers of water surrounding it, andwill timely find its way back into the centre. As explained above, thissystem is further aided by the use of the pulsing pump 20 whichcirculates water around the tank 10 at an appropriate rate, the coolerwater from the bottom of the central container being pumped out to theoutermost layer 16 to be heated by the solar energy. The connecting pipe21, of pulsing pump 20, connected to the central container can befurther extended in the central container 14 to extract water found atabout the same level as where the warmer water is situated. By the timethe hot water reaches the pump 20, it will lose its heat to thesurrounding cooler water found at the base of the containers. It is alsopreferable to connect the other end of the connecting pipe 21, connectedto the outermost layer, to the side of the apparatus which will beexposed to the sun. The frequency and the quantity of water to becirculated can be selected by the user or alternatively, it can be doneautomatically using a microprocessor and a system of temperature sensorsplaced strategically around the tank 10. The pulsing rate of the pumpwill depend on which of the various embodiments of the invention isused, as described hereafter together with their pathway for the flow ofwater, and also on the climate in which the apparatus is being used, forexample, the climate in the northern part and southern part of atemperate zone will require different pulse rates.

The apparatus can be further made more efficient by connecting the coldwater inlet 19/305 directly to the base of the central container. If thecold water inlet 19 is connected to the top of the outermost layer asshown in FIG. 1, in operation, the apparatus may pulse heated water fromthe central container 14 out to the outermost layer 16. This heatedwater, now in the outermost layer, may lose a portion of its heat ifthere is no sun shining on the apparatus, which would be undesirable.

In order to avoid this situation, and to make the apparatus moreefficient, the cold mains supply 19 may connect directly to the base ofthe central container 14. As shown in FIG. 3, when the user draws waterfrom outlet 332 of the central container 301, the solenoid switch 330and the pump 320 are switched on simultaneously. The pump will pulse outsubstantially all water as it enters the central container 301, from thecold main supply 305, to the outermost space layer 303 and as a result,will push/suck heated water from the other space layers into the centralcontainer 301. This ensures that only water from the cold mains supply19/305, and no heated water, is pulsed out of the central container14/301 to the outermost layer via connecting pipe 321/21. A solenoidswitch 30/330 may be used to operate the cold mains supply 19/305 and asecondary switch may be used to operate the pump 21/320.

Alternatively, using this same configuration of the cold mains supply19/305, when the user draws water from outlet 32/332, the solenoid30/330 can be switched on, for a period, to allow an amount of coldwater to enter and settle at the base of the central container 14/301.The pulsing pump 20/320 is then switched on to pump the cold watersettled at the base of the central container 14/301 out to the outermostlayer 16/303 of the apparatus, and by action will also tend to push/suckhot water, found in the layers surrounding the central container,through inlet 37/437 into the central container 14/301. The pump 20/320and the solenoid 30/330 may also use other sequences as separate devicesto regulate the temperature of the water in the apparatus or the centralcontainer accordingly.

FIG. 8 shows an alternative construction of the apparatus enabling waterto flow tortuously into the inner container 14 using a differentpathway. Inlet openings 837 and 835 are constructed on opposite sides ofcontainers 14 and 12 respectively, at a level about mid-way length fromthe base of the central container. The chimney 29, openings 37, 35 ofthe embodiment are no longer present. When the pump 20 is put intoaction, the water sucked into inlet 835 and 837 will be the less denseand faster moving warmer water formed mostly in the top half part of theapparatus of space layers 16, 17 and 18 (the top half part being abovethe openings 837 and 835). This ensures that less cool water, if thereis any present, does not migrate into the adjacent space layers (andultimately into the inner container) to cool the water found therein.Previously, this unwanted cooling effect may occur because of inlets 37,35 being situated at the base of the apparatus.

This dynamic insulation system described enables the temperature of thewater in the central container to be kept at a usable temperature notonly during the day but also during the evening and night byappropriately pulsing the pump 20 to move the heat that has escaped intothe outer layers back into the central container 14.

The apparatus can also accommodate a micro-furnace 60 to heat water inthe central container 14 if necessary, such as during the night, whenthere is not enough sunlight during the day or when the user needs waterat a higher temperature than the normal operating temperature of theapparatus. The micro-furnace 60 works together with the dynamicinsulation system to help provide hot water to the user when solarenergy alone will not suffice. A suitable type of micro-furnace has beenproposed in document WO 85/02899 entitled “Gas Immersion Heater”. Thisshown a water heating apparatus which uses a gas burner to heat water inthe tank. It also discloses a system of using water layers asinsulation. However, this system is prone to ultimately lose anycaptured heat as, while a portion of the heat lost by the central tankis captured in the surrounding jacket of water, the warmer water fromthe jacket cannot flow into the central tank until water is drawn offfrom the central tank. Again, the water might be too cool by the time itis needed. Alternatively, the micro-furnace may be operated by means ofan electric heater.

As mentioned previously, the water in the central container 14 has atemperature profile from warmer water at its top to cooler water at itsbottom. Water heated by the micro-furnace 60 in the central containerwill lose a portion of its heat to its surrounding space layers 18, 17and 16. This portion of “lost” heat can be returned to the centralcontainer by pulsing pump 20 appropriately (as before). Thus, thepreheated water which migrates into the central container 14 will needvery little gas heating to establish the acceptable hot watertemperature if not already at that temperature.

The micro-furnace 60 consists of the primary metal tube 40 having au-shaped secondary metal tube 22. The metal tube 22 further consists ofa third tube 23 also in a u-shape to act as a gas supply. The metal tube22 is sealed to be airtight on one end, whereas the other end found inthe central container 14 is left open to accommodate for a burner flame26 arising from tube 23. Tube 23 can be affixed to the secondary tube 22by bolts placed at a small distance apart. Metal tube 22 is alsosupplied with air through air supply 24 which can be aided in operationusing an air blower 25.

The burner flame 26 may comprise a pilot light and/or a main light,which is very common in the industry. The pilot light in itself may formpart of the heating mechanism and may mostly be used to increase theamount of hot water in the apparatus when the temperature in the top ofthe central container 14 is sufficiently high. The pilot light may alsoserve to increase the amount of usable hot water when very little isdrawn off, e.g. at night. The main light, which may be controlledautomatically or manually by a thermo-couple switch and/or temperaturesensors in the apparatus, will switch on when the device has an overallloss of hot water due to baths or other uses. Alternatively the burnerflame 26 can be lit using an electrical method such as a peizo-electricigniter. The pilot light burner flame can be lighted by removing cap 41to access the burner and can use a separate or the same gas tube supplyas the main light burner flame. The cap 41 is preferably madetransparent to be able to view the burner/pilot light before removingcap 41.

The burner flame 26 creates hot gases which then release their heat inthe primary metal tube 40 to heat the water in the central container 14.These combusted gases and any other residues will find their exit waytowards the open end 27 of metal tube 40 (due to cap 41 being present onthe other end). The open end of tube 40 preferably uses a constricteddesign to avoid draught air which could lead to a flameout condition. Aremovable or fixed collection tray may also be provided for collectingany deposition of condensate and acids from the burning gas. It is verylikely that the collection tray will not need emptying often, asevaporation will take place. Furthermore, in this embodiment of themicro-furnace 60, it is also preferable to have an outlet such a hole ora plurality of small holes in tube 22, directly below the burner flame26, to let any condensate out.

The micro-furnace 60 can further accommodate in space 33 safety andflame guard features that are known in the industry, such as overheating detection, flame cut out or power cut out devices. For example,if the temperature in any part of the apparatus reaches a thresholdlevel (for example 75° C.), the flameout switch will operate, which inturn cuts out the gas supply. In case of using a pilot light and/or mainlight, the gas supply tube(s) may have a cut-off valve that cuts the gassupply to the tube(s), in the event that the flame ever blows out, orthe apparatus is overheated.

FIG. 7 shows a different embodiment of the micro-furnace 60. Metal tube740 now contains the secondary tube 722 with its open end 760 formed atan angle in relation to the metal tube 740. The burner flame 26 is nowcloser to the metal shell of 740 and delivers heat directly to the shellof metal tube 740 and not to the atmosphere inside the tube. This heatsup water in the inner container 714 quicker and more efficiently.

It is also preferred that in the construction of FIG. 8, the opening 837and 835 are formed just below the level at which the burner flame 26 issituated.

The apparatus in an alternative embodiment can have more than onemicro-furnace 60 and can accommodate one or more burner flame 26 in eachmicro-furnace 60.

The apparatus described herein is designed to maintain hot water createdfrom solar energy should that be available or gas energy at any othertime and to avoid the heat, which has been heated by any other source,to escape.

It is preferable to make the water move faster when in the layersclosest to the outermost drum 11 than when in the layers closest to thecentral container 14. This ensures the system heats water quickly andefficiently by the solar rays. FIG. 1 shows an example of thisconfiguration where the space layers 16 are thinner than space layer 17which in turn are thinner than space layer 18. In one embodiment, eachadjacent outer space layer is half as thick as the previous layer.Furthermore, it is also preferable to make the water move faster nearthe top of the apparatus, because more heat is dissipated by the hotwater at the top of the apparatus, and therefore spaces 16, 17 and 18may be made thinner at the top than at the bottom.

The apparatus can be further made more efficient by adding thermalinsulating material 15 to surround the outer shells of all the innercontainers 13, 13 and 14, including the whole of the chimney 29 goinginside the central container 14. This insulation inhibits the transferof heat to neighbouring layers of water. It is preferable to also havethe top and bottom insulation thicker than on the sides. FIG. 2 shows anon-dynamic thermal insulation 53 present around the outer shell ofoutermost container 11 of approximately seven inches thick. Thisnon-dynamic insulation 53 consists of a sliding door 52 which can beopened to expose at least 50% of the tank to the outside environment.The opening and closing of the door 52 can be controlled using a lightsensor monitoring the amount of sunshine available together withtemperature sensors present in the tank to optimise the efficiency ofthe device. When in a closed position, such as at nights, thisnon-dynamic insulation 53 will prevent heat escaping from the tank 10.It is also preferable to embed the pipes surrounding the apparatus, suchas the cold water inlet supply and/or the hot water outlet pipes, withinthe non-dynamic thermal insulation.

In the case where the sliding door 52 of the non dynamic insulation isopen and heat is being transferred to the apparatus from the sun, anywarm water pumped out of the central container 14 to the outermost layerwill tend to absorb heat from the sun in the outermost layer 16. Shouldthe doors 52 be closed, however (at night for example) the pulsating ofwater in the central container 14 will also tend to lower the “level” ofthe hotter water towards the base, by bringing more hot water,previously heated in the surrounding layers, inside the centralcontainer 14. This may cause colder water to gather in the outer layers,but in time an equilibrium will be set up inside the apparatus,particularly as little hot water is likely to be drawn at night.

Bleed valves 28 are present on each container to remove any air bubblesformed in the process.

In operation, the hot supply 32 connects to various outlets in the housefor distribution of hot water, such as the sink 31 a, basin 31 b or bath31 c. A release valve 38 is also connected to hot supply 32 and is keptopen when all the other outlets are closed. This ensures that pressureis not built up in the apparatus due to expansion of the heated water.By triggering a switch in the bathroom for hot water, the user opensboth the solenoid switch 30 and a relay switch 31 c in the bathroom.This will allow cold water from supply 19 to enter the tank and heatedwater in the tank will move in a torturous manner to push hot water outof the central container to the hot water supply 32 to the bathroom.

FIG. 3 shows a second embodiment of the invention, where the apparatusconsist of a central container 301 which has a hollow jacket 540 wrappedin layers 302 around it. The hollow jacket 540 may surround the centralcontainer 301 completely or partially. A main cold water supply 305controlled by a solenoid switch 530 connects to the base of the centralcontainer 301. A water pump 320 also connects the base of the centralcontainer 301 to the outermost layer 303 formed by the jacket. Thecentral container 301 also has an inlet 437 to allow water from thejacket 540 to enter the central container 301. An outlet 332 is used todraw water from the central container by the user to distribute wateraround as described in the previous embodiment.

At the start of operation, the central container 301 and the jacket 540(FIG. 5) is filled with water from the cold mains supply 305, helped bythe pump 320. The jacket 540 will comprise an absorber portion 501 onits outermost layer 303 which will be exposed to sun rays. Water in theabsorber portion 501 of one end 503 of the jacket 504 will be heated bysun rays and can flow into the central container 301 by using openinginlet 437 at the inner end 502 of the jacket.

In operation, the water in the inner layers closer to the centralcontainer 301, formed by the wrapped jacket 540 will usually containmore heat than the water contained in the layers closer to the outermostlayer 303. When water is drawn from the tank by the user, the solenoid330 controlling the cold main supply 305 and the pump 320 aresimultaneously switched on. The pump 320 will pump water that hadearlier entered the central container 301, from the cold main supply, tothe outermost space layer 303 and as a result will push heated water,mostly found in the top section of the apparatus, from the jacket 540into the central container 301, through inlet 437. The hot water fromthe central container can thus be accessed by the user through 332. Thewater remaining in the outermost layer 303 will be heated by the sun.

The pulsing pump 320 may also be used to flow/circulate water around theapparatus to move the heated water from the central container 301 to theoutermost layer 303 as described in the first embodiment. This can applyin any situation when it is beneficial to do so, such as at the start ofoperation of the apparatus when there is a lot of cold water in theapparatus. It is also preferred to have a system of temperature sensorsplaced around the apparatus to optimise the rate of pulsing of the pump320. For example, a temperature sensor can be placed at the base of thecentral container 301, where the pump 320 normally is, to monitor thetemperature and operate the pump accordingly.

The cross section of the jacket is preferably in the shape of asymmetrically flattened round tube, wrapped around the outer shell ofthe central container 301. FIG. 6 shows a preferred cross section shapeof the material with the water space 601. Furthermore, it may bepreferable to provide the apparatus with metal straps, such as copper,around it or by placing the apparatus inside an outer container toprevent the apparatus from collapsing due to pressure, such as in caseswhen water inside the apparatus expands. This is particularly importantwhen the jacket 540 is long, thus forming a large number of layers 302.The outer container preferably having recesses/holes formed in its wallsto allow sun rays to reach and heat the outermost layer 303 of theapparatus. It is also desirable to use some type of attachment means,such as studs, to secure together adjacent layers formed by the jacket,again to make the apparatus more rigid.

The jacket is preferably wrapped around the central container 301 suchthat it forms one or more layers 302 (as shown in FIG. 3), with eachlayer formed adding to the thickness of the material wrapped around thecontainer 301. In a preferred embodiment, the jacket 540 is about 2.54cm×75 cm×457 cm and is shaped in one piece with the hollow water space601 inside. It is also preferable to use a corrugated plastic material,such as polypropylene, which is able to withstand the forces in thissituation. As shown in FIG. 9, in one embodiment, the jacket may beprovided with spacers 901 moulded or bonded thereto and may beconstructed in one piece or several pieces joined together.

FIGS. 10 a and 10 b are schematic drawings showing in more detail thejacket 540 wrapped around the central tank 1014 together with insulation1016 to form a spiral water pathway, as seen more clearly form FIG. 10b. The apparatus is further contained in an outer container 1018 and theside facing north of the outer container is provided with furtherinsulation 1020.

A preferred method to manufacture and assemble the jacket with theinsulation will now be described. In this preferred embodiment, thejacket covers the top 1022 of the central tank 1014 to form asemi-spherical dome around the top and is assembled in a plurality oflayers/joins. Preferably, a portion of the circumference of the smallestspiral path formed is flush with the external circumference of thecentral tank.

FIG. 11 shows the method used to manufacture the first (smallest) spirallayer formed by the jacket 540. FIG. 11 shows a base 1101 with a centraltube 1103 arranged near the middle of the base. Preferably, the tube hasa circular cross-section to accommodate the circular tube of themicro-furnace explained before. A plurality of formers 1105, are spacedapart, preferably equally, around the central tube 1103. The formers arepreferably all flush with the base 1101, as shown. Preferably, theformers are built using card or plywood.

Each former has the same shape but are sized differently. Former 1 isslightly smaller than former 2, which is slightly smaller than former 3so that former 9 is the largest former used to manufacture the firstspiral layer. Each former is larger in dimensions than the previousformer in both the x-axis and the y-axis directions, as shown in FIG.12. Preferably, the difference in sizes between formers follow a linearinterpolation (for example B-A divided by 7) between the largest and thesmallest former to form intermediate formers so that a smooth regularmould or pattern may be achieved for manufacturing the spiral layers.The number of intermediate formers used is not important so as long asenough is used to be able to form a pattern that will be used to shapethe layers.

Each spiral layer comprises insulation 1016 which, in turn, comprisestwo layers of plastic walls 1024 and 1026, preferably fibre glass. Whentwo or more spiral layers are joined together, a spiral pathway 1028 forwater between the two fibre glass walls is formed. Preferably, in eachlayer, the layer of insulation is 16 mm, each layer of fibre glass is ⅔mm and the layer for water to travel is about 10 mm, such that thedifference between the former 1 and 9 in the direction of the y-axis,shown by C, is about 30 mm. Each revolution therefore increases inheight by approximately 30 mm.

FIG. 13 shows the formers of FIG. 11 suitably covered to form a patternfor manufacture of the first spiral layer. It is preferably covered withplaster or clay but any other method can be used so that a smoothregular pattern (following the dimensions of the formers) can beobtained. The first spiral layer comprises only one layer of fibre glassand is preferably moulded over the pattern in the following sequence:the insulation followed by the layer of fibre glass.

The second and subsequent spiral layers are manufactured in the same wayusing larger patterns accordingly and include two layers of fibre glasseach. Each subsequent layer is preferably moulded over the patternfollowing the sequence; a first layer of fibre glass, the layer ofinsulation, the second layer of fibre glass.

The last former of each spiral layer is the first former to be used tofor the pattern of the next layer. For example, former 9 is the lastlargest former for the first spiral layer built, and a similar sizedformer is used as the first smallest former of the second layer to bebuilt.

The plurality of insulated spiral layers built are joined together attheir corresponding ends to form an insulated jacket comprising a spiralwater path connecting the outermost spiral layer to the innermost spirallayer and a central opening to accommodate the micro-furnace.

It is understood that each former follows substantially the profile ofthe shape of the final jacket desired, for example in this case asemi-archway shape is used for the formers. It is also understood thatthe smallest former of the first layer is sized such that after thefirst layer is formed it may accommodate the central tank 1014 within itor the assembled jacket.

Preferably, a valve is used at the inlet 437 to ensure that water flowsin only one direction, into the central container.

Preferably, the apparatus in this embodiment is held in a structure,such as a barrel to avoid any deformation in shape of the apparatus.

This apparatus in this embodiment can also accommodate one or moremicro-furnace 60 with one or more burners incorporated, similar to theone described for the first embodiment.

The apparatus in all embodiments may also incorporate baffles 580 insidethe tank to stop swirl mixing of water inside the central container,when water is introduced into the central container. In case where thecold water supply 305/19 is situated at the base of the centralcontainer, the baffles ensure that newly introduced water tends to stayin the lower section of the central container.

The apparatus in all embodiments can be placed inside a protective domewith at least part of the dome allowing sun rays to reach the sunexposed part of apparatus. The dome may be made of a transparentmaterial, such as glass or Perspex. Preferably an air gap is leftbetween the dome and the apparatus to act as further insulation. Thedome will stop any blowing air or breeze to influence the apparatus,making it more efficient, and the dome may also be used to add to theaesthetics of the apparatus. The air inlet to the air blower 25 and theconstricted opening 27 to allow gases to exit the micro-furnace 60 arepreferably situated outside the dome.

The above embodiments are for illustration only and other embodimentsand variations are possible and envisaged without departing from thespirit and scope of the invention. It should also be clear to theskilled person that any features described in the content of oneembodiment may equally be applicable to any of the other embodiments, ifappropriate.

1. A solar water heating apparatus comprising a central tank and one ormore outer layers, said outer layers also forming water pathways,wherein, when substantially filled with water, said water is able tocirculate around a path formed by said central tank and at least one ofsaid one or more outer layers, and wherein at least part of the exteriorof the outermost layer is adapted to be exposed to the sun, in use. 2.The apparatus as claimed in claim 1 wherein said apparatus is arrangedsuch that water is able to circulate between the outermost layer and thecentral tank via any intermediary layers.
 3. The apparatus as claimed inclaim 1 wherein pumping means may be provided to circulate the water. 4.The apparatus as claimed in claim 3, wherein said pumping means is apulsing pump.
 5. The apparatus as claimed in claim 3 wherein saidpumping means is arranged to operate continuously or intermittently. 6.The apparatus as claimed in claim 3, wherein said apparatus comprises acontroller means to control said pumping means depending on sensed watertemperature at predetermined points in the apparatus.
 7. The apparatusas claimed in claim 1, wherein said tank and/or the outer layerscomprise a plastic material.
 8. The apparatus as claimed in claim 7,wherein said plastic material is polypropylene or a similar material. 9.The apparatus as claimed in claim 1, wherein said tank and/or the outerlayers comprise a metallic material.
 10. The apparatus as claimed inclaim 9, wherein said metal is copper or a similar material.
 11. Theapparatus as claimed in claim 1, wherein said at least one layerscomprises one or more outer tanks around said central tank.
 12. Theapparatus as claimed in claim 11, wherein said outer tanks comprisewater outlet(s)/inlet(s) at opposing points to adjacent tanks, toprovide a tortuous path for said water to circulate.
 13. The apparatusas claimed in claim 1, wherein said at least one layers comprises ahollow jacket wrapped at least once around said inner tank.
 14. Theapparatus as claimed in claim 13, wherein the cross section of saidjacket may be in the shape of a symmetrically flattened round tube. 15.The apparatus as claimed in claim 1, wherein said apparatus comprises acold water input and warm water output.
 16. The apparatus as claimed inclaim 15, wherein said warm water output is drawn from said centraltank.
 17. The apparatus as claimed in claim 16, wherein said output isdrawn from a point at or above halfway from the bottom of the centraltank.
 18. The apparatus as claimed in claim 15, wherein said cold waterinput feeds into the outermost layer of the apparatus.
 19. The apparatusas claimed in claim 15, wherein said cold water input feeds into thebottom of the central tank.
 20. The apparatus as claimed in claim 1,wherein said apparatus comprises insulation around its outside, of whichat least a portion of which is arranged to move so as to expose anuninsulated portion of the outside of said apparatus to allow for directsolar heating.
 21. The apparatus as claimed in claim 20, wherein saidinsulation is arranged to move based on the time of day, readings from atemperature sensor, readings from a light sensor, or a combinationthereof.
 22. The apparatus as claimed in claim 20, wherein saidinsulation may simply be arranged to be moved manually.
 23. Theapparatus as claimed in claim 1, wherein said apparatus furthercomprises a gas burner apparatus.
 24. The apparatus as claimed in claim23, wherein said gas burner apparatus is substantially immersed in saidtank.
 25. The apparatus as claimed in claim 23, wherein said gas burnerapparatus is arranged, in normal use, to burn an amount of gascomparable to that of a domestic pilot light flame.
 26. The apparatus asclaimed in claim 23, wherein said gas burner has a further setting toburn gas at a greater rate for fast heating.
 27. The apparatus asclaimed in claim 23, wherein the flame of said gas burner apparatus islocated at a point approximately half way from the bottom of the centraltank.
 28. A water heating apparatus comprising a central tank and anauxiliary heating element, said auxiliary heating element beingsubstantially immersed in said central tank, and wherein at least partof the exterior of said apparatus is adapted to be exposed to the sun soas to heat the contents by solar energy, in use.
 29. The apparatus asclaimed in claim 28, wherein said apparatus is made of a plasticmaterial.
 30. The apparatus as claimed in claim 29, wherein said plasticis polypropylene or a similar material.
 31. The apparatus as claimed inclaim 28, wherein said apparatus further comprises one or more outerlayers, said outer layers also forming water pathways, wherein, whensubstantially filled with water, said water is able to circulate arounda path formed by said central tank and at least one of said one or moreouter layers.
 32. The apparatus as claimed in claim 31, wherein saidapparatus is arranged such that water is able to circulate between theoutermost layer and the central tank via any intermediary layers. 33.The apparatus as claimed in claim 31, wherein said at least one layerscomprises one or more outer tanks around said central tank.
 34. Theapparatus as claimed in claim 33, wherein said outer tanks may comprisewater outlet(s)/inlet(s) at opposing points to adjacent tanks, toprovide a tortuous path for said water to circulate.
 35. The apparatusas claimed in claim 31, wherein said at least one layers comprises of ahollow jacket wrapped at least once around said inner tank.
 36. Theapparatus as claimed in claim 35, wherein the cross section of saidjacket is in the shape of a symmetrically flattened round tube.
 37. Theapparatus as claimed in claim 31, wherein pumping means may be providedto circulate the water.
 38. The apparatus as claimed in claim 37 whereinsaid pumping means comprises of a pulsing pump.
 39. The apparatus asclaimed in claim 37, wherein said pumping means is arranged to operatecontinuously or intermittently.
 40. The apparatus as claimed in claim37, wherein said apparatus further comprises controller means to controlsaid pumping means depending on sensed water temperature atpredetermined points in the apparatus.
 41. The apparatus as claimed inclaim 28, wherein said apparatus comprises a cold water input and warmwater output.
 42. The apparatus as claimed in claim 41, wherein saidwarm water output is drawn from said central tank.
 43. The apparatus asclaimed in claim 42, wherein said warm water output is drawn from apoint at or above halfway from the bottom of the central tank.
 44. Theapparatus as claimed in claim 41, wherein said cold water input feedsinto the bottom of the central tank or alternatively into the outermostlayer.
 45. The apparatus as claimed in claim 28, wherein said apparatuscomprises insulation around its outside, of which at least a portion ofwhich is arranged to move so as to expose an uninsulated portion of theoutside of said apparatus to allow for direct solar heating.
 46. Theapparatus as claimed in claim 45, wherein said insulation is arranged tomove based on the time of day, readings from a temperature sensor,readings from a light sensor, or a combination thereof.
 47. Theapparatus as claimed in claim 45, wherein said insulation is simply bearranged to be moved manually.
 48. The apparatus as claimed in claim 28,wherein said auxiliary heating element is a gas burner apparatus, and isarranged, in normal use, to burn an amount of gas comparable to that ofa domestic pilot light flame.
 49. The apparatus as claimed in claim 48,wherein said gas burner has a further setting to burn gas at a greaterrate for fast heating.
 50. The apparatus as claimed in claim 48, whereinthe flame of said gas burner apparatus may be located at a pointapproximately half way from the bottom of the central tank.
 51. Theapparatus as claimed in claim 28, wherein said an auxiliary heatingelement is an electric immersion heater, having a power outputcomparable to a domestic incandescent light bulb.
 52. (canceled) 53.(canceled)